This invention relates fuel control systems for automobile engines and more particularly to an improvement in a solenoid used in such a system.
With the need to control automobile engine operations so to improve fuel economy, reduce emissions and still achieve good driveability, various schemes have been developed to control the air-to-fuel ratio of the mixture produced in a carburetor and supplied to an engine. Many such schemes use an auxiliary air bleed to vary the pressure in a fuel circuit of the carburetor. By controlling the quantity of auxiliary air bled into a fuel circuit the quantity of fuel supplied to a air passage of the carburetor can be controlled and hence the ratio of the resultant mixture. Control of the air bleed has typically been accomplished using a pulsed solenoid.
Since most carburetors utilize two separate fuel circuits; one for high speed engine operation and the other for low or idle speed operation, systems previously employed have used two separate solenoids, each controlling an air bleed to each separate fuel circuit. This is because the two fuel circuits are subjected to vastly different vacuum signals; the high speed circuit being subjected to a signal measured in inches of water (H.sub.2 O) and the low speed circuit being subjected to a signal measured in inches of mercury (Hq). Were one solenoid used to control air bleed to both systems, the idle speed circuit would create a slight depression in the air bleed path for the high speed circuit and the resultant air-fuel mixture produced with the high speed circuit would be richer than it should be. At the same time however, the capability of using only one solenoid to control both bleeds would produce economies of cost, simplify circuitry and overall reduce system complexity.